Synthesis, characterization and electrophosphorescent properties of mononuclear platinum(II) complexes based on 2-phenylbenzoimidazole derivatives

The rational design, synthesis and characterization of five phosphorescent platinum complexes [(C boolean AND N) Pt(acac)] [Hacac = acetylacetone, HC boolean AND N = 1-methyl-2-(4-fluorophenyl)benzoimidazole (H-FMBI), 1-methyl-2-phenylbenzoimidazole (H-MBI), 1,2-diphenyl-benzoimidazole (H-PBI), 1-(4-(3,6-di-t-butylcarbazol-9-yl)) phenyl-2-phenylbenzoimidazole (t-BuCz-H-PBI), and 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))carbazol-9-yl) phenyl-2-phenylbenzoimidazole (t-BuCzCz-H-PBI)] have been discussed. The crystal structure of (MBI) Pt(acac) shows a nearly ideal square planar geometry around Pt atom and the weak intermolecular interactions with pi-pi spacing of 3.55 angstrom. All of the complexes emit green phosphorescence from the metal-to-ligand charge-transfer (MLCT) excited state with high quantum efficiency (0.08-0.17) at room temperature.

Synthesis, photophysical and electrophosphorescent properties of mononuclear Pt(II) complexes with arylamine functionalized cyclometalating ligands

Four cyclometalated Pt(II) complexes, i.e., [(L-2)PtCl] (1b), [(L-3)PtCl] (1c), [(L-2)PtC CC6H5] (2b) and [(L-3)PtC CC6H5] (2c) (HL2 = 4-[p-(N-butyl-N-phenyl)anilino]-6-phenyl-2,2'-bipyridine and HL3 = 4-[p(-N,N'-dibutyl-N'-phenyl)phenylene-diamino]-phenyl-6-phenyl-2,2'-bipyridine), have been synthesized and verified by H-1 NMR, C-13 NMR and X-ray crystallography. Unlike previously reported complexes [(L-1)PtCl] (1a) and [(L-1)PtC CC6H5] (2a) (HL1 = 4,6-diphenyl-2,2'-bipyridine), intense and continuous absorption bands in the region of 300-500 nm with strong metal-to-ligand charge transfer ((MLCT)-M-1) (d pi(Pt) -> pi*(L)) transitions (epsilon similar to 2 x 10(4) dm(3) mol (1) cm (1)) at 449-467 nm were observed in the UV-Vis absorption spectra of complexes 1b, 1c, 2b and 2c.

Supramolecular architectures, photophysics, and electroluminescence of 1,3,4-oxadiazole-based iridium(III) complexes: From mu-dichloro bridged dimer to mononuclear complexes

One mu-dichloro bridged diiridium complex and three mononuclear iridium(III) complexes based on the 1,3,4-oxadiazole derivatives as cyclometalated ligands and acetylacetonate (acac) or dithiolates O,O'-diethyldithiophosphate (Et(2)dtp) or N,N'-diethyldithiocarbamate (Et(2)dtc) as ancillary ligands have been synthesized and systematically studied by X-ray diffraction analysis. The results reveal that three mononuclear complexes all adopt distorted octahedral coordination geometry around the iridium center by two chelating ligands with cis-C-C and trans-N-N dispositions, which have the same coordination mode as the diiridium dimer. The dinuclear complex crystallizes in the monoclinic system and space group C2/c, whereas three mononuclear iridium complexes are all triclinic system and space group P(1) over bar. In the stacking structure of the dimer, one-dimensional tape-like chains along the b-axis are formed by hydrogen bondings, which are strengthened by pi stacking interactions between phenyl rings of 1,3,4-oxadiazole ligands. Then these chains assemble a three-dimensional alternating peak and valley fused wave-shape structure. In each stacking structure of three mononuclear complexes, two molecules form a dimer by the C-H center dot center dot center dot O hydrogen bondings, and these dimers are connected by pi stacking interactions along the b-axis, constructing a zigzag chain.

Synthesis, crystal structure, and magnetic properties of {[Cu(oxbe)]Mn(H2O)[Cu(oxbe)(DMF)]}(n)center dot nDMF center dot nH(2)O: From dissymmetrical mononuclear entities to a 3D heterometallic supramolecular coordination polymer

Self-assembly of the building block [Cu(oxbe)](-) with Mn(II) led to a novel coordination polymer {[Cu(oxbe)]Mn(H2O)(Cu(oxbe)(DMF)]}(n).nDMF.nH(2)O, where H(3)oxbe is a new dissymmetrical ligand N-benzoato-N'-(2-aminoethyl)-oxamido and DMF = dimethylformamide. The crystal forms in the triclinic system, space group P(1)over-bar, with a = 9.260(4) angstorm, b = 12.833(5) angstrom, c = 15.274(6) angstrom , alpha = 76.18(3)degrees, beta = 82.7(3)degrees, gamma = 82.31(3)degrees, and Z = 2. The crystal structure of the title complex reveals that the two-dimensional bimetallic layers are constructed of (CuMnII)-Mn-II-Cu-II chains linked together by carboxylate bridge and hydrogen bonds help to produce a novel three-dimensional channel-like structure. The magnetic susceptibility measurements (5-300 K) were analyzed by means of the Hamiltonian (H)over-cap = -2J(S)over-cap (Mn)((S)over-cap(Cu1) + (S)over-cap(Cu2)), leading to J = -17.4 cm(-1).

From dissymmetrical mononuclear entities to centrosymmetrical heterotrinuclear complex with 2D supramolecular structure: synthesis, characterization, crystal structure, and magnetic properties

A new centrosymmetrical heterotrinuclear complex, {[Cu(oxbe)](2)Co(H2O)(2)}.2DMF.DMA with 2D supramolecular structure, has been obtained by the self-assembly of a dissymmetrical building block [Cu(oxbe)](-) with bivalent metal ion Co2+, where H(3)oxbe is dissymmetrical ligand N-benzoato-N'-(2-aminoethyl)oxamido, DMF = dimethylformamide, DMA = dimethylamine. Its structure was determined by single crystal X-ray analysis. The molecular structure is centrosymmetrical with the cobalt atom lying on an inversion center. Through the hydrogen bonds and d-pi stacking interactions, a 2D supramolecular structure is formed. This study exemplifies a new method for the assembly of supramolecular structure using a dissymmetrical brick. Magnetic susceptibility measurements (5-300 K) indicate that the central cobalt and terminal copper metal ions are antiferromagnetically coupled with J = -23.1 cm(-1).

Syntheses and crystal structures of mononuclear rhodium hydrido complexes from the reactions of [Rh(H)(2)(PPh3)(2)(EtOH)(2)]ClO4 with various nitrogen ligands

Reactions of the Rh hydrido complex [Rh(H)(2)(PPh3)(2)(EtOH)(2)]ClO4 (1) With nitrogen ligands such as 2-(4-thiazolyl)benzimidazole (tbz). pyridazine (pdz), imidazole (im) and pyrimidine (pmd) in CH,Cl, afforded Various mononuclear Rh hydrido complexes, [Rh(H)(2)(PPh3)(2)(tbz)]CIO4 (2), [Rh(H)(2)(PPh3)(2)(pdZ)(2)]ClO(4)(.)2CH(2)Cl(2) (3). [Rh(H)Cl(PPh3)(2)(pdz)(2)](ClO4CH2Cl2)-C-. (4). [Rh(H)(2)(PPh3)(2)(im)(2)]ClO(4)(.)2CH(2)Cl(2) (5). [Rh(H)Cl(PPh3)(2)(im)(2)](ClO4CH2Cl2)-C-. (6). [Rh(H)(2)(PPh3)(2)(pmd)(2)](ClO4CH2Cl2)-C-. (7) and the Rh non-hydrido complex [RhCl2(pmd)(4)]ClO4 (8). The Rh complexes 2. 3, 5 and 6 were crystallographically characterized. The formation process was monitored by H-1 NMR and UV-Vis spectra. In all the Rh hydrido complexes, the Rh atom is coordinated by two PPh3. ligands in trans-positions and two nitrogen ligands in the cis-positions. The remaining sites Lire occupied by one or two hydride atoms to form a saturated 18-electron framework in a slightly distorted octahedral geometry. For complex 2 an appreciable inter-molecular pi interaction is observed between planes of tbz and PPh3 ligands, while an intra-molecular hydrogen bonding interaction between C-H and Cl atoms is found in complex 6.

Synthesis and structure of a novel mononuclear tungsten (VI) citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)]

The first mononuclear tungsten-citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)] (1) has been prepared by the reaction of ammonium tetrathio tungstate and lithium citrate in CH3OH - H2O solution at pH 8.2. There are two crystallographically independent anions in the asymmetric crystallographic unit. The crystal structure of the title compound (triclinic, space group P (1) over bar, a = 6.901(1), b = 15.136(3), c = 16.107(3) Angstrom, alpha = 75.85(3), beta = 89.89(3), gamma = 89.97(3), V = 1631.4(6) Angstrom (3), R = 0.068, R-w = 0.1674 for 3878 reflections with I > 2 sigma (1)), reveals that in the compound a tungsten atom is coordinated to a fully deprotonated citrate as a tridentate ligand and three terminal oxygen atoms to form a distorted coordination octahedron.

Kinetics and Force Dependence of P-selectin/PSGL-1 Interactions Measured by AFM

Leukocytes roll along the endothelium of postcapillary venules in response to inflammatory and thrombotic processes. The rolling under hydrodynamic shear forces is a first step in directing leukocytes out of the blood stream into sites of inflammation and is mediated by the selectins, a family of extended, modular, and calcium-dependent lectin receptors. The interactions between P-, E-or L-selectins and their count.

Mechano-Chemical Coupling at Molecular Level: Forced Dissociation of Selectin/Ligand Binding

Mechano-chemical coupling is a common phenomenon that exists in various biological processes at different physiological levels. Bone tissue remodeling strongly depends on the local mechanical load. Leukocytes are sheared to form the transient aggregates with platelets or other leukocytes in the circulation. Flow pattern affects the signal transduction pathways in endothelial cells. Receptor/ligand interactions are important to cell adhesion since they supply the physical linkages...

Kinetic measurements of cell surface E-selectin/carbohydrate ligand interactions

Selectin/ligand interactions initiate the multistep adhesion and signaling cascades in the recruitment of leukocytes from circulation to inflamed tissues and may also play a role in tumor metastasis. Kinetic properties of these interactions are essential determinants governing blood-borne cells' tethering to and rolling on the vessel wall. Extending our recently developed micropipette method, we have measured the kinetic rates of E-selectin/ligand interactions. Red cells coated with an E-selectin construct were allowed to bind HL-60 or Colo-205 cells bearing carbohydrate ligands. Specific adhesions were observed to occur at isolated points, the frequency of which followed a Poisson distribution. These point attachments were formed at the same rate with both the HL-60 and Colo-205 cells (0.14 +/- 0.04 and 0.13 +/- 0.03 mum(2) s(-1) per unit density of E-selectin, respectively) but dissociated from the former at a rate twice as fast as did from the latter (0.92 +/- 0.23 and 0.44 +/- 0.10 s(-1), respectively). The reverse rates agree well with those measured by the flow chamber. The forward rates are orders of magnitude higher than those of Fc gamma receptors interacting with IgG measured under similar conditions, consistent with the rapid kinetics requirement for the function of E-selectin/ligand binding, which is to capture leukocytes on endothelial surfaces from flow.

Effects of Molecular Length, Ortientation and Amino Acid Mutation on Kinetics of Selectin/Ligand interactions

Receptor/ligand interactions are basic issues to cell adhesion, which are important to many physiological and pathological processes such as lymphocyte-mediated cytotoxicity, tumor metastasis and inflammatory reactionl. Selectin/carbohydrate ligand bindings have been found to mediate the fast rolling of leukocytes on activated endothelial monolayer. Kinetic rate and binding affinity constants are essential determinants of cell adhesion...

Low Spring Constant Regulates P-Selectin-Psgl-1 Bond Rupture

Forced dissociation of selectin-ligand bonds is crucial to such biological processes as leukocyte recruitment, thrombosis formation, and tumor metastasis. Although the bond rupture has been well known at high loading rate r(f) (>= 10(2) pN/s), defined as the product of spring constant k and retract velocity v, how the low r(f) (< 10(2) pN/s) or the low k regulates the bond dissociation remains unclear. Here an optical trap assay was used to quantify the bond rupture at r(f) <= 20 pN/s with low k (similar to 10(-3)-10(-2) pN/nm) when P-selectin and P-selectin glycoprotein ligand 1 (PSGL-1) were respectively coupled onto two glass microbeads. Our data indicated that the bond rupture force f retained the similar values when r(f) increased up to 20 pN/s. It was also found that f varied with different combinations of k and v even at the same r(f). The most probable force, f

Impact of carrier stiffness and microtopology on two-dimensional kinetics of P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) interactions

Mechanics and surface microtopology of the molecular carrier influence cell adhesion, but the mechanisms underlying these effects are not well understood. We used a micropipette adhesion frequency assay to quantify how the carrier stiffness and microtopology affected two-dimensional kinetics of interacting adhesion molecules on two apposing surfaces. Interactions of P-selectin with P-selectin glycoprotein ligand-1 (PSGL-1) were used to demonstrate such effects by presenting the molecules on three carrier systems: human red blood cells (RBCs), human promyelocytic leukemia HL-60 cells, and polystyrene beads. Stiffening the carrier alone or in cooperation with roughing the surface lowered the two-dimensional affinity of interacting molecules by reducing the forward rate but not the reverse rate, whereas softening the carrier and roughing the surface had opposing effects in affecting two-dimensional kinetics. In contrast, the soluble antibody bound with similar three-dimensional affinity to surface-anchored P-selectin or PSGL-1 constructs regardless of carrier stiffness and microtopology. These results demonstrate that the carrier stiffness and microtopology of a receptor influences its rate of encountering and binding a surface ligand but does not subsequently affect the stability of binding. This provides new insights into understanding the rolling and tethering mechanism of leukocytes onto endothelium in both physiological and pathological processes.

IL-8-induced L-selectin shedding regulates its binding kinetics to PSGL-1

L-selectin plays a crucial role in inflammation cascade by initiating the tethering and rolling of leukocytes on endothelium wall. While many L-selectin molecules are rapidly shed from the cell surface upon activation, the remaining membrane-anchored L-selectin may still play an important role in regulating leukocyte rolling and adhesion with different binding kinetics. Here we developed an in vitro model to activate Jurkat cells via interlukin-8 (IL-8) and quantified the two-dimensional (2D) binding kinetics, using a micropipette aspiration assay, of membrane-anchored L-selectin to P-selectin glycoprotein ligand 1 (PSGL-1) ligand coupled onto human red blood cells (RBCs). The data indicated that L-selectin shedding reduced the amount of membrane-anchored L-selectin and lowered both its reverse and forward rates. These results suggested that the rolling dynamics of activated leukocytes was determined by two opposite impacts: reducing the surface presentation would enhance the rolling but lowering the kinetic rates would decrease the rolling. This finding provides a new insight into understanding how L-selectin shedding regulates leukocyte rolling and adhesion.

Heterodimerization of integrin Mac-1 subunits studied by single-molecule imaging

Heterodimerization of integrin Mac-1 (alpha(M) beta(2)) Subunits plays important role on regulating leukocytes adhesion to extracellular matrix or endothelial cells. Here, using total internal reflection microscopy, we investigated the heterodimerization of integrin Mac-1 subunits at the single-molecule level in live cells. Individual alpha(M) subunit fused to the enhanced yellow fluorescent protein (eYFP) was imaged at the basal plasma membrane of live Chinese hamster ovary (CHO) cells. Through analysis of mean square displacement (MSD), diffusion coefficient, the size of restricted domain and fraction of molecules undergoing restricted diffusion, we found that as compared with the diffusion in the absence of beta(2) subunit, the diffusion of single-molecule of alpha(M)-YFP was suppressed significantly in the presence of beta(2) subunit. Thus, based on the oligomerization-induced trapping model, we suggested that in the presence of beta(2) subunit, the am subunit may form heterodimer with it. (C) 2008 Elsevier Inc. All rights reserved.